Bryan Connolly finds a new dogwood cross for New Jersey.
Last summer, while working as a consulting botanist for the Environmental Protection Agency’s National Wetland Condition Assessment project in Allamuchy Township, New Jersey, I found an unusual colony of shrubby dogwood in the genus Swida (previously known as Cornus). The research plot was in a seasonally flooded meadow, with broad-leaved cattail (Typha latifolia), ironweed (Vernonia noveboracensis), and reed canary grass (Phalaris arundinacea) present. The site was previously cleared and looked to have a long history of human disturbance. The location is now set aside as town open space, and secondary succession is occurring, with woody plants increasing in dominance. Swida, or shrubby dogwoods, are known as old-field colonizers, and also as wetland species. There were two species present at this locality, S. racemosa, gray dogwood, and S. amomum, silky dogwood. In my experience, S. racemosa is more of an old-field colonizer, while S. amomum tends to favor wetlands. The area was both an old field and a wetland, and so it made sense that the species were co-occurring and abundant at the site.
I noticed one Swida colony that did not cleanly fit into either S. racemosa or S. amomum. Swida racemosa generally has narrow (lanceolate) leaves, white fruit, gray bark, white pith, and upright growth habit; while S. amomum has broader (ovate) leaves, red- dish-purple bark, brown twig pith, blue fruit, and a mounded growth form. The atypical plant I spotted had S. racemose characters, including narrow leaves 2.5–3.8 cm wide and verrucose gray bark on the older stems, but also displayed the S. amomum traits of blue fruit and brown twig pith. Additionally, the growth form was unusual: it was a tall plant, about 2–3 m in height, and somehow both upright and mounded, intermediate between the habits of S. racemosa and S. amomum. The pedicels or flower stalks were also reddish-maroon, not the typical bright red of S. racemosa. With this combination of characters, I thought it was likely to be a hybrid of the two species. From my experience working with coauthors on The Vascular Plants of Massachusetts: A County Checklist, I remembered a Swida hybrid, though I couldn’t recall the parental species or if it was named. Additionally, from my wanderings and botanical work in the Northeastern US, I have published many new records of hybrid taxa—and I could not place this plant among them.
After a long day in the field I returned to my hotel room, fired up Go Botany (the online database of the Native Plant Trust), and confirmed that S. racemosa and S. amomum do in fact hybridize. On the account of my vague Swida hybrid recollection and my previous encounters with hybrid taxa, I wasn’t surprised that a cross was known, but was glad that my hybrid hypothesis was supported by the literature. To my delight, the hybrid was listed as a nothospecies (a direct hybrid of two species) with the name Swida × arnoldiana. The original description, by Alfred Rehder, was made in 1905 from a row of shrubs growing at the Arnold Arboretum.
This individual could just represent variation found within S. racemosa, which occasionally can have brown pith or light blue fruit. But I find it unlikely that a plant would exhibit both these traits while also co-occuring with plants that have the morphology of S. racemosa and S. amomum. I thus believe this plant to be S. × arnoldiana. If I am correct, then it is a state record for New Jersey! According to Flora of North America, the hybrid has only been found in Massachusetts, Missouri, Ohio, and Pennsylvania.
I have published many new records of hybrid taxa—and I could not place this plant among them.
The specimen voucher will be deposited at the Arnold Arboretum herbarium. This unique hybrid individual spotted in the field offered a nice little puzzle to solve—and it was gratifying to learn that it is named after a wonderful arboretum I know and love!
Bryan Connolly is an assistant professor in biology at Eastern Connecticut State University.
Thanks to the ESS Group, Inc. scientists James Treacy, Joe Bertherman, and Heidi Fisher.
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